Guide

Corten steel in the garden: pre-rusting, patina and care

Know-how from the workshop

Corten steel with rust patina and the word Corten

Corten steel is alive. Its warm, rust-brown surface is not a coating; it is created by wind and weather and changes over the years. Here we explain how the protective patina forms, what «pre-rusted» means, which colour differences are normal in the first months and how you can even out stains or scratches yourself.

How the patina forms

We work corten steel in its bright rolled state, that is, metallic grey. Only then can it be precisely laser cut, folded, welded and ground. The typical rust colour only develops afterwards outdoors: the constant alternation of wet and dry first creates a loose layer of rust. Underneath it, on weathering steel, a dense barrier layer grows over time that protects the steel from rusting through. Ordinary structural steel cannot do this and keeps on rusting. You can read more about the material under Corten steel & custom laser designs.

In our climate it usually takes one to three years for the even, chestnut-brown rust surface to form. The process is never entirely finished: depending on the season, rain and sun, the colour continues to change slightly later on. That is exactly what makes corten steel so lively in the garden.

Delivered pre-rusted: what it means

Many customers want the rust colour from the start. That is why we can deliver corten steel raised beds and planters pre-rusted on request: we start the rusting process in our workshop in Etzgen. Your planter arrives with a clearly visible rust surface.

Good to know: pre-rusting is a preliminary stage. The patina is not yet fully formed and the surface is not yet sealed; the protective oxide layer only develops outdoors in the weather over the following years. Allow at least one week of additional delivery time for pre-rusting.

You can choose the «Deliver pre-rusted» option directly in the raised bed calculator and see the price instantly.

What is normal in the first months

Young corten steel is never completely even. These effects are part of the material, are not a defect and even out with weathering, usually within a few months and at the latest after around three years:

  • Colour differences between individual sheets: even parts mounted right next to each other can look different at first, depending on the material batch, mill scale, sun and orientation.
  • Streaks from running water: where rainwater runs off unevenly or collects, the surface changes colour differently.
  • Dark to black stains: these form when the young surface stays damp without air, for example under packaging or under fallen leaves.
  • Marks: straps, supports during transport or the vacuum lifters used during processing can leave marks that often only become visible once the steel starts to rust.
  • Scratches: small scratches from transport or installation rust over again with time.

After delivery: the essentials

  • Remove film and packaging immediately so that no moisture is trapped underneath.
  • Store parts dry until installation, with air between them, not lying flat on top of each other.
  • Regularly remove leaves and objects lying on the surface.
  • At first, rust water running off can stain light-coloured paving. With light slabs, plan for a base or a strip of gravel.

Evening out stains, marks and scratches yourself

With an ordinary kitchen sponge (one rough and one soft side) you can easily even out the young surface:

  1. Roughen: rub the affected area with the rough side of the sponge or with coarse sandpaper. This loosens the loose rust layer. Always work in the direction in which rainwater runs off.
  2. Moisten: wet the soft side generously and wipe the surface with it, again always in the direction of the rainwater.
  3. Wait: the colour evens out within a few hours. If necessary, repeat after a few days.

This also lightens dark stains and lets scratches «rust away», so the surface becomes uniform more quickly.

Prefer an even colour?

If a completely even surface matters to you, corten steel is not the right choice. It develops slight nuances throughout its life. As an alternative, we make the same in stainless steel with a powder coating in your RAL colour, for example RAL 8015 chestnut brown. In the raised bed calculator, choose «Powder-coated stainless steel».

Corten steel at INOXMETALL

Questions about your corten steel piece? We will be happy to advise you personally, or visit our showroom in Etzgen, which is open around the clock.